Fix flags for darwin's gcc which is actually clang
Fix flags for darwin's gcc which is actually clang

wugh7125/ortp,jiangjianping/ortp,caizw/ortp,Linphone-sync/oRTP,carpikes/ortp,videomedicine/oRTP,carpikes/ortp,VTCSecureLLC/ortp,jiangjianping/ortp,videomedicine/oRTP,wugh7125/ortp,wugh7125/ortp,caizw/ortp,VTCSecureLLC/ortp,Linphone-sync/oRTP,caizw/ortp,Distrotech/oRTP,jiangjianping/ortp,carpikes/ortp,Linphone-sync/oRTP,videomedicine/oRTP,VTCSecureLLC/ortp,Distrotech/oRTP,Distrotech/oRTP